Improve CLI behaviour regarding stdin, stdout, stderr etc for better pipelining and interaction with other scripts and tools

[TristanSpeakEasy]

• Implement support for stdin to allow openapi specs to be piped into the CLI as an alternative to passing via arguments for pipelining between commands and other tools
• Revisit and refactor handling of stdout and stderr to better allow pipelining and managing output from the tool
• Revisit command arguments and refactor as necessary to make them as robust and compatible with the wider ecosystem as possible

[TristanSpeakEasy]

#151

[TristanSpeakEasy]

completed